Hello hc,
You'll find that the French MAS 49 mags and the French LMG mags are much like the BAR and FAL mags ie very wide at the front and using two sets of feed small lips. I believe that your AK mag will require verticle clearance at the front for the rotating bolt lugs (unlike the BAR, FAL, MAS 49 types).

That front verticle clearance issue and narrow area breach seem to indicate either an M-14, a MG-13, or a Hakim (or Danish Ljungman) box.

1biggun thanks for those barrel links - I never would have thought about Numrich! That's half what a PAC-NOR barrel runs, and I can obviously lathe it down to fit the profile!

Quick magazine update - we hand-cycled the longest factory loads we could find - 140 grain - which was 2.98" length. Below the max COL but still factory load. The MG13 magazine does *NOT* work for 6.5x55 in that it is too long by about 3/8" or so. That extra length is enough that when the rounds begin to ride forward in relation to the round below them, they tend to tip downward from the push of the bolt when the shoulder is pushed that far forward.

We ordered a pack of those IMA 7.5mm French mags for the French 1924/29 MG:

According to my Hornady manual, that round measure just a little bit longer than the 6.5x55. I'm hoping that it will be close enough to keep the rounds from doing that slide-and-tip thing in the mag. So once they ship the mags I'll have more info.

Chamber pressures should be on the relatively low side of .308, as he doesn't load these incredibly hot. So I am inclined to say that the RPK parts will be adequate due to all the comparison of the Yugo .308 bolt vs. the 7.62x39 bolt (remember all that talk!?!?). Since this is relatively less pressure than the .308, I believe it should be fine. However I can't seem to find a readily available pressure table of the different loads that are available. He's running the 100 grain rounds - almost the smallest rounds for that cartridge.

THOSE PRESSURES ALL SEEM REASONABLE TO ME FOR A BUILD ON A YUGO TRUNION. WOULD BE LESS THAN A 308. ONE OF THOSE FRONT END ASSEMBLIES FROM CFS WOULD BE A GOOD START. IF YOU USE A SPORTING WEIGHT BARREL A L1A1 GAS BLOCK WOULD LIKELY BE PRETTY CLOSE TO THE RIGHT ID. OF COURSE IF YOU COULD FIND A SAIGA 308 THEN YOU COLD REALLY UP THE PRESSURES TO MATCH THE 260 REM PERFORMANCE. THIS WILL BE A GOOD LONG RANGRE SHOOTER IF LOADED WITH 142 GR HPBT BULLETS. BY LONG RANGE IM TALKING OVER 800 YARDS.

I hade a chance to buy the whole gun for $350 a while back and noticed how the mag attached and thought that it would be a neat way to hold a mag on a 308 conversion an not loose so much trigger guard space. as one could eleminate the whole latch and spring. I wish I had bought the gun it may still be there. it was mint.

There is the Swedish 6.5x55 BAR called the "Kg m/37". It's a BAR but the magazine is curved, not straight like other BAR magazines. The Swedish BAR magazine is normal 6.5x55 length at the bottom but get longer at the receiver so might not be a good choice.

It's accurate what it says about military headspace being longer than SAAMI headspace. I had a virgin m/38 Mauser barrel I fitted to an m/96 Mauser receiver. The headspace measured long without any reaming of the chamber. I turned the barrel shoulder back to tight SAAMI headspace. I think the factory chamber might have been perfect with military gauges even though the barrel had never been on a receiver before. The barrel didn't have any sights on it so I could turn it tight anywhere I wanted. The link also says there were at least two different military headspace standards.